The study areas were elected according to their history of seismic activity. The case studies were chosen, when considering the seismic resistance applied elements; the existent typological characteristics; the vernacular morphology, and the current preservation of these strategies. The fact is that population, sometimes, had a preventive response, based on their past recurrent experiences. In other cases, the population just had reactive responses to the seismic event, especially if there had not been frequent past seismic occurrences. On the other hand, local builders are the true leaders of the vernacular architecture efforts in their villages and regions. Therefore, it is the vernacular architecture, which reveals, more clearly, the existence of a Local Seismic Culture
Conclusively, it is assumed that a portion of the Local Seismic Culture, including both, the preventive or reactive response, is influenced either by the intensity of the earthquakes, or by the frequency of earthquakes in the region; or both
The process of region selection was based on the following criteria, considering Ferrigni’s (1990) relevance to the LSC definition: 1) the impact per region, of the earthquakes of higher intensity, though less frequent; 2) the frequency of the earthquakes of low and moderate intensity; and 3) the quantity and consistency of the observed retrofitting structural solutions
The buildings that had three or more identified reinforced techniques were considered as having reactive measures applied. When a group of a minimum of three buildings shared common features, then Local Seismic Culture was identified in the region
Based on the materials and the techniques to repair and to retrofit damage of in-use vernacular buildings, related to local population reactive or preventive efforts to earthquake occurrence, specific case studies were selected for a deeper research
Reference case – The Lisbon downtown
The 1755’s earthquake in Portugal is an obvious reference, given the extensive damage across the country, with emphasis on the town of Lisbon, the national capital.Therewassignificantpublishedinformationonthe earthquake damage, from written observation immediately following the earthquake, as the Marquis of Pombal requested a damage status from all the parishes in the country. Thus, the 1755 earthquake, and all the planning addressed in Lisbon, in terms of rebuilding the city’s downtown, as well as the damage status requested throughout the country, emerged as a basis of reference for the development of the project. The reconstruction process of the Lisbon downtown set a new conceptual and technological seismic approach in Portugal. The applied strategies and techniques influenced many of the new coming constructions, especially the ones located at seismic prone areas. With more or less complexity, many local building cultures appropriated some of the ‘pombalino’ solutions, adjusting them to their regional conditions. The ‘gaioleiro’ (cage) system is perhaps the greatest manifestation of its influence in the Portuguese vernacular heritage
Region 1 (R1) – Tagus Lezíria
The Tagus Lezíria region is situated in a high intensity seismic area. The region is also characterised by the occurrence of relevant earthquakes, as it is located near the fault line of ‘Vale Inferior do Tejo (VIT)’
The village of Benavente was selected as a case study, especially due to the fact that there had occurred three major earthquakes, 1531, 1909 and 1914, of which the epicentres were located near this village. The earthquake of 1909 had important consequences in Benavente. According to local bibliographic data, the earthquake left destruction, or in partial ruin, a significant part of the village buildings (Vieira, 2009). Some years later, the village of Benavente, was reconstructed, but in general, there was new housing. However, some of the reconstructed houses integrated seismic resistant techniques, such as, the Pombalino system, as well as symmetrical patterns (Vieira, 2009). Horizontal reinforcement on the houses was also observed. In regards to the preventive and reactive seismic reaction, Benavente is based on the use of the two approaches: a) The reactive reaction, because there was no previous concern, before the 1909’s earthquake; b) The preventive reaction, as elements of seismic resistance were incorporated in some of the new construction
Region 2 (R2) – Coastal Alentejo
The Coastal Alentejo region is a high intensity seismic area.
After some investigation and fieldwork, Alcácer do Sal was selected as a case study. The village is characterised as an area of high intensity and regular seismic activity. In the region, old buildings have been found with pombalino walls, (Correia & Merten, 2001). Horizontal reinforcement of the houses and the use of buttresses and tie-rods were also observed
The earthquake of 1858 was one of the most important ones that affected the Portuguese mainland. The area was severely affected, and the village of Melides was partially destroyed. Following field missions, the village of Melides was also selected as a case study, due to historic and regular seismic activity, but also due to the identification seismic reinforcement in buildings. A constructive culture is based on the improvement of material properties of the constructive systems. As a reaction to the effects of earthquake, the population presented reactive solutions through the use of structural seismic resistant features, such as horizontal reinforced walls, buttresses, tie-rods, and reinforced plinth course. embasamento saliente? N é este o termo, é: reinforced plinth course
Region 3 (R3) – Central Alentejo
The Central Alentejo region never suffered from the consequences of a severe earthquake. However, the region has been exposed to numerous earthquakes of medium intensity that produced minor damage to buildings, and created memories of fear and panic in the population
During the initial fieldwork, it was possible to identify evidence of seismic prevention, through the placement of seismic resistant elements, such as, counter arches,inspecificbuildings.Therefore,theÉvoraHistorical Center was also selected as a case study, due to several evidences, especially, the use of seismic resistant features, as a reaction to the various events. The historical centre has implicit evidence of strengthened buildings, through the use of counter arches, buttresses and wall reinforcements
Region 4 (R4) – Lower Alentejo
The historical seismicity on the Lower Alentejo region can be characterised as frequent, but of medium intensity, with the intensities of earthquakes growing during the twentieth century. This region is characterised by the use of preventive response. There was a probable reaction to various events, and an implicit need for strengthening of the buildings. Along the lower Alentejo, it was observed, during several field missions, the use, in several houses, of isolated elements of reinforcement, such as stiffeners, buttresses and reinforced plinth courses. The villages of S.Brissos, Baleizão e Trindade, near the municipality of Beja, constitute good examples of such approach
Region 5 (R5) – The Algarve
The Algarve is illustrated by a strong historical seismicity with earthquakes that caused major damage. The 1719’s earthquake in the Portimão area had a maximum intensity of IX; the 1722’s earthquake on the coast of Tavira had a maximum intensity of X; and the 1856’s earthquake in Loulé had a maximum intensity of VIII
In the survey missions carried out in the Algarve region, several reinforcement techniques were identified on the vernacular architecture, such as buttresses, tie-rods and pombalino walls. Lagos, Tavira and Vila Real de Santo António emerged as relevant case studies, due to consistent architectural evidence, although they represent completely different approaches to the earthquake hazards
Region 6 (R6) – The Azores
Based on the literature review (historic seismic occurrences and damages), and a mission to the Azores Islands, the islands of Terceira and Faial emerged as case studies. The islands are located in a complex area with an intense volcanic activity, near the boundary of 3 tectonic plates, referred to as the Azores triple junction (Nunes et al. 2004), Terceira is in a high intensity seismic area with numerous earthquakes. The 1980’s earthquake, according to the collected data, had extensive destructive consequences to communities throughout the island, but particularly in Angra do Heroismo.